A lithium ion secondary battery generally has a configuration in which carbon, a lithium-transition metal complex oxide, and a mixture of carbonate esters are used for the negative electrode, the positive electrode, and an electrolytic solution, respectively. Since carbonate ester used for the electrolytic solution is not easily oxidized or reduced by water or other organic solvents, and can obtain a higher voltage, the lithium ion secondary battery has a higher energy density and a higher capacity than a nickel-hydrogen battery, which is an aqueous battery. Therefore, the lithium ion secondary battery is widely distributed as a secondary battery for notebook-type personal computers, mobile phones, video cameras, and digital still cameras.
Since a laminate-type lithium ion secondary battery in which a laminate film, such as an aluminum laminate film, is used for an exterior has a light weight and a large energy density, which results from a large fraction of an active material in the battery, the laminate-type lithium ion secondary battery is widely used.
Since the laminate-type lithium ion secondary battery has a weaker strength than a battery covered with a metal can, the voltage applied to a battery element becomes weak. Therefore, when the electrode is expanded and shrunk due to repetition of charging and discharging of the battery, there is a problem in that the inter-electrode distance between the positive electrode and the negative electrode becomes uneven due to the above fact, and thus the ion conductivity and the electric current density become uneven, whereby the capacity is degraded.
With respect to this problem, a technology in which the inter-electrode distance is kept constant by providing a resin having an adhering force between the positive electrode and the negative electrode, and degradation of the capacity due to repetition of charging and discharging is suppressed has been suggested.
For example, Japanese Patent No. 4099969 describes a battery in which a porous resin is formed on the surface of an electrode by floating a porous endothermic insulating resin in the electrode on the surface of the electrode by spinodal decomposition or a micelle method.